For example, compounds represented by the following general formula are known as fluorine-containing polyether compounds having a functional groups at the molecule terminals:

Patent Document 1 JP-A-11-343336
Furthermore, compounds represented by the following formula are known as more popular compounds resulting from oligomerization of the main chain structures of the above-mentioned compounds:

Patent Document 2 JP 2,990,646
It is said that the compounds represented by these general formulae can give elastomeric moldings having much distinguished characteristics (chemical resistance, heat resistance, and low-temperature characteristics) by a fluorine-containing organohydrogen siloxane compound having a plurality of Si—H groups in the molecule and a platinum compound catalyst, and the elastomeric moldings are durable even if used under low-temperature conditions, particularly at about −50° C., without losing the flexibility. Furthermore, it is said that curable compositions containing these compounds as the main component have a remarkable moldability, enabling even RIM molding. However, the cured products have siloxane bonds in the intramolecular cross-linking structure, so, if used in the presence of an acidic substance such as hydrogen fluoride, etc., chemical deterioration and the consequent reduction in the mechanical strength sometimes undesirably takes place.
On the other hand, for example, vinylidene fluoride/tetrafluoroethylene/perfluoro(methyl vinyl ether) terpolymer as popular fluorine-containing elastomer having distinguished low-temperature characteristics have a glass transition temperature Tg of about −25° C. to about −35° C. Furthermore, fluorine-containing elastomers having a glass transition temperature Tg of −35° C. or lower, obtained by copolymerization of perfluoro vinyl ether compounds having perfluoro(alkoxyalkyl) group side chains, as given below, in place of perfluoro(methyl vinyl ether) are also known:
CF2═CFO(CF2)3OCF3 
CF2═CFO(CF2)2O(CF2)nCF3 (n:1-4)
CF2═CFO(CF2CF2)mOCF3 (m:1-5)
CF2═CFO(CF2CF2CF2O)nCmF2m+1 (n:1-4, m:1-5)
CF2═CFO[CF2CF(CF3)O]nCF3 (n:2-6)    Patent Document 3: U.S. Pat. No. 5,969,216    Patent Document 4: U.S. Pat. No. 6,294,627    Patent Document 5: JP-A-64-52733    Patent Document 6: JP-A-2004-348087
Fluorine-containing elastomers obtained by copolymerization of these perfluoro vinyl ethers have a good chemical resistance, e.g. resistances in the presence of an acidic substance such as hydrogen fluoride, etc., and also have a good heat resistance, but the moldability is still on a level equivalent to that of the usual fluorine-containing elastomers.